The present invention relates to an auto document feeder for use with a duplex copying machine, and more particularly to an auto document feeder which permits automatic feeding of sheet originals having images on both sides to an exposure station of the duplex copying machine in the order of the pages.
Recently, duplex copying, namely the making of copies having images on both sides, has been studied by use of an electrophotographic copying apparatus.
In performing such duplex copying, particularly when duplex copies are made from sheet originals, in comparison with the conventional one-side copying, more care must be taken in setting such sheet originals in a duplex copying machine because, when setting duplex sheet originals in the copying machine, with respect to the order of pages, and inside and outside or top and bottom of each duplex sheet original, more mistakes are apt to occur.
Furthermore, as in the case of the conventional one-side copying, it is time-consuming to set such duplex sheet originals manually. Also, particularly in the case of printed sheet originals having images or letters on both sides, they must be reversed or inverted in order to make copies therefrom, so that the copying procedure becomes more complicated and accordingly mis-copying will occur more frequently.
Thus, for example, the following sheet-feeding devices have been developed. One device feeds sheet documents from a sheet original input tray to an exposure station and discharges the used sheet documents to a sheet original output tray and stacks them on the output tray. In such a sheet-feeding device, when all the sheet originals have been discharged to the output tray, they must be placed in the input tray again.
Another device comprises a sheet original input tray, and a sheet original output tray which can be used as another input tray as well. In this device, after sheet originals are fed from the input tray to the exposure station for exposure, they are discharged to the output tray and the discharged sheet originals are then fed from the output tray to the exposure station.
In the former device, it is troublesome to replace the used sheet originals from the output tray to the input tray. Furthermore, in both the former device and the latter device, the output tray has to be provided besides the input tray. Particularly, in the case of the latter device, sheet-feeding means, such as sheet-feeding rollers, have to be incorporated. Due to such requirement, the latter device is apt to become expensive and oversized.